1. Field of the Invention
The invention relates in general to a device making it possible to regulate the intensity of the electric current traversing a receiver, and more particularly to regulating the current in an incandescent lamp.
2. Description of the Prior Art
Conventionally, lighting regulators, also known as dimmers, operate according to the principle of the chopping of the sinusoid of the AC current distributed. As is known, the current of the mains supply is a sinusoidal AC current, of frequency 50 or 60 Hertz depending on the country, and of voltage 220 to 240 volts, or 110 to 120 volts.
This chopping of the sinusoid is achieved by means of a triac or two associated thyristors mounted in series with the lamp or the receiver in question, the circuit thus formed being closed across the terminals of the AC supply voltage. In fact, this triac cuts the current which traverses the filament of the lamp in time with the period of the current. This principle of cutting known as "phase monitor" makes it possible to achieve good regulation of light intensity, from almost 0 to 100% of the latter. In fact, to obtain a very low light intensity, close to 0, the closing of the triac is controlled with a phase lag of almost 180.degree. with respect to the voltage. To obtain a light intensity half the maximum light intensity, the closure of the triac is undertaken with a phase lag of 90.degree. with respect to the voltage, and finally to obtain maximum illumination, the triac is permanently closed. In fact, it is appreciated that such a method, which is simple to embody and inexpensive, makes it possible easily to control lamps up to powers of 1,000 Watts.
Nevertheless, it has various disadvantages. Firstly, there is no electrical isolation between the lamp and the main power supply, resulting in the need to earth the metallic parts of the controlled lamp. Now, in domestic usage, the earth sockets are not distributed throughout the dwelling.
Furthermore, with such a device, the lamp is subject directly to the main voltage. Hence, this type of supply cannot operate with low-voltage lamps, such as in particular 12 volt halogen lamps, widely available for domestic usage.
Finally, the shape of the electric current which traverses the filament of the lamp is not sinusoidal, bearing in mind the chopping performed by the triac, and the fast variations in the intensity of this current when closing the controlled on/off switch cause interference as well as harmonics of the frequency of the supply voltage. The latter phenomena "pollute" electricity distribution networks all the more since, on the one hand, the numbers of regulators of this kind are growing rapidly and, on the other hand, the unit powers of the lamps thus controlled have increased with the significant spread of 220 volt halogen lamps. This "pollution" may prove troublesome for certain types of domestic electrical appliances, such as in particular television sets, washing machines, ovens, etc., comprising electronic control and monitoring circuits.